The present invention relates to a ball joint for parts of a motor vehicle steering or wheel suspension and, more particularly to a ball joint comprising a radially flexible bearing shell consisting of plastic material, a joint pin having a spherical head configured to be received in the bearing shell and retained with an outer circumference thereof in a recess of a joint housing, a cylindrical portion of circumferential surfaces of the bearing shell sized and configured to bear against a cylindrical wall portion of the recess, the bearing shell enclosing the spherical head beyond an equatorial diameter thereof located within the cylindrical wall portion, and a retaining member inserted into the recess and securing the bearing shell with prestress in the recess.
A known ball joint is disclosed in German Patent No. 2,235,874 in which a bearing shell, starting from the shell edge, is provided with slots which are provided at equal angular distances from one another and extend along a respective generatrix and the length of which corresponds essentially to the axial length of the cylindrical part of the shell circumference or to half the axial length of the bearing shell. This permits the plastic bearing shell enclosing the spherical head of the joint pin beyond its equatorial diameter to be attached onto the spherical head.
The bearing shell is fixed in the housing recess by a slotted spring ring forming a retaining member. This spring ring is seated in an annular groove put into the inner wall of the housing recess, is supported on the bearing-shell end face interrupted by the slots and thereby exerts an axially directed pressing force in the main load direction of the ball joint, i.e. in the direction of the bottom of the housing recess, on the legs of the bearing shell which are formed by the shell slots.
Under the effect of this pressing force, the shell legs experience a compressive load. As a result, the shell legs are deformed and are in surface contact with the outer surface of the spherical head in particular regions only due to tolerances present between the faces of the ball casing, the bearing legs and the cylindrical wall portion of the housing recess. The result of this is that, in spite of the pressing force exerted permanently on the bearing shell by the spring ring, the radial play between the spherical head and bearing shell caused by their wear increases over the service life of the ball joint and consequently high fluctuations at the moment of friction are unavoidable. This impairs, for instance, the vibrational decoupling via transverse-link rubber bearings, in that, in a ball joint used, for example, as a supporting joint, the coupling between a wheel carrier and a transverse link is correspondingly reduced as a result of the decreasing moment of friction.
As a further consequence of the pressing force exerted on the bearing shell, the spherical head of the joint pin is clamped in the bearing shell such that a breakaway moment has to be overcome in order to pivot it.
UK Patent No. 2,104,590 A discloses a ball joint having a radially slotted bearing shell which receives the spherical head and which is arranged coaxially with a cylindrical part of the circumferential surface in a cylindrical recess of the joint housing formed by a sheet-metal sleeve. Formed onto the bearing shell on both sides of the cylindrical part of the circumferential surface are conical circumferential-surface parts, of which one bears against an elastic sealing ring and the other against an elastic thrust ring.
In the assembled state, the sealing ring is supported on an inner flange of the sheet-metal sleeve, while a closing cover crimped into the sheet-metal sleeve is supported on the thrust ring. Also, a radial distance is provided between the cylindrical circumferential-surface part of the bearing shell and the inner circumference of the sheet-metal sleeve. When the closing cover is being crimped in, the bearing shell therefore cannot be prestressed in a specific way in the radial direction, since the material of the thrust ring and sealing ring creeps.
An object on which the present invention is based is to improve a ball joint of the aforementioned type such that the radial guidance of the spherical head in the bearing shell remains largely constant in the main load direction of the ball joint over its service life and that a desired moment of friction can be applied to the spherical head.
This object has been achieved according to the present invention by providing that the bearing shell has a slot passing therethrough and extending transversely relative to the circumferential direction, wherein the bearing shell is radially prestressed relative to an axis of the cylindrical wall portion between cylindrical wall portion in the recess and the equatorial diameter of the spherical head.
The configuration and arrangement of the bearing shell according to the present invention guarantee that, due to its radial prestress, the bearing shell bears constantly against the spherical head of the joint pin in a play-free manner.
A displacement of the spherical head within the bearing shell, brought about by shell wear which occurs, can now take place only coaxially relative to the cylindrical edge portion located on the housing side as a result of the radial prestress of the bearing shell between the cylindrical wall portion in the housing recess and the equatorial diameter of the spherical head. However, the initially set moment of friction between the equatorial diameter of the spherical head and the bearing shell thereby remains largely constant.
Another feature of the present invention affords the advantage that, in the event of abrasion of the bearing shell in the main load direction of the ball joint, the inner annular edge, supporting the spherical head, of the shell orifice narrowing conically inwards experiences wear, thus leading to an increase in the diameter of the shell orifice, but at the same time to a reduction of the surface pressure in the orifice region of the latter. Moreover, this features also offers the advantage that a desired trend of the moment of friction can be determined for the ball joint in relation to the bearing-shell wear, for which purpose the conicity of the bearing-shell orifice is to be determined arithmetically.
Another feature of the present invention affords the advantage that the bearing shell previously already prestressed in a specific way in the radial direction, together with the spherical head received by the latter, and, having been preassembled complete in the flanged bush, can be inserted into the recess of the joint housing. The only further operation remaining is to crimp the housing collar so as to fix the flanged bush receiving the bearing shell firmly to the housing.
Further features of the present invention afford the advantage that the casing portions of the bearing shell, which enclose the spherical head, but which are not received with radial prestress by the flanged bush, are nevertheless kept in contact with the casing of the spherical head in a gap-free manner. The same effect is achieved in another embodiment of the present invention such that the annular collar of the flanged bush is capable of being used at the same time for an advantageous sealing of the joint housing at the exit point of the joint pin.
In a further embodiment of the present invention, the parts of the flanged bush engaging over the spherical head and the annular collar consist of plastic, with the result that the weight of the flanged bush can be reduced.
Yet still another embodiment of the present invention has the advantage that the bearing shell has to be introduced only with its cylindrical circumferential-surface part into the flanged bush, with the elastically flexible retaining segments of its plastic shaped body at the same time enclosing the spherical head over a further circumferential region. Also, a reliable securing of the joint pin against coming loose from the joint housing can be achieved in a simple way.